HP Compaq 6735S - No power / No charge

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  • mushy408
    New Member
    • Nov 2010
    • 9
    #1

    HP Compaq 6735S - No power / No charge

    Hey all! Firstly, this site is amazing! I've been looking for something like this for a while. I hope I can input some of my knowledge to others as I have quite a bit of experience with laptop motherboards.

    I've been working for a PC shop for over 12 months now repairing laptops & consoles at component level so I've learnt quite a bit.

    I've been trying to isolate a fault on this laptop board for some time now.

    The laptop in question is:
    HP/Compaq 6735S

    Original fault was a dry joint on the DC socket. I've been trying to get this laptop (buy it) off my friend for ages. Since then he's had "Someone who knows about computers" have a look at it.

    Anyways, I've got it now. No power, not even from battery. I've stripped it down and traced the input voltage around the board to various areas.

    I've resoldered the DC socket & also replaced a LM393 which was burnt. Still not getting any charge/power LEDs.
    Whilst 'probing' I felt a hotspot with my hand - TPS51120 - Synchronous Buck Controller (charge controller) This IC gets HOT as soon as power is inserted.

    From looking at the datasheet, it seems that this IC is is responsible for charging the battery and switching to AC when charged (duh!)

    My first few tests had me checking the surrounding caps - 1 short
    I removed the shorted Cap and still have a short across the pads which to me indicates the IC is damaged - hence the heating up

    I have seen a number of laptops with similar problems ESPECIALLY after having a bad DC socket. The constant switching of the power supply (Charger making contact, then breaking) over a space of time slowly burns out these controllers until either the battery refuses to charge, or the laptop refuses to power up.

    What I'm asking is has anyone else had this problem? What/how did you repair it? This isn't MOSFET or TRENCHFET related

    I can upload pictures if needed.

    Thanks!
    Tags: None
    • meanderer
      Senior Member
      • Jul 2010
      • 50
      #2
      Re: HP Compaq 6735S - No power / No charge

      repairing laptops at component level? good skills you have there.

        Comment

        • sebuncle
          Member
          • Jun 2010
          • 46
          • France
          #3
          Re: HP Compaq 6735S - No power / No charge

          Hello,i have the same problem on a hp 6735b .It will not start no lights.
          I looked on Q500 after power connector pins 1 to 4 have 19v and pins 4 to 8 have 0v. If I shunts pin 1 with 5 the laptop starts and works normally with the power button. If I remove the shunts intensity drop and the laptop shutdown . i don't find the real failure
          JOVY RE7500

            Comment

            • marcellodj
              Senior Member
              • Nov 2010
              • 99
              #4
              Re: HP Compaq 6735S - No power / No charge

              Hello,
              i have similar issues with this model; power on, leds on, but no sign of life.Battery led is off, i tried to reflow all bga on the board, without success, so may be power ic related.Any help?

                Comment

                • Dave24v
                  New Member
                  • Aug 2013
                  • 6
                  • England
                  #5
                  Re: HP Compaq 6735S - No power / No charge

                  Did anyone ever find out this problem in the end?

                  I have the same problem on mine, ... No light's , no power, no nothing!!

                  I've checked for dry solder joints etc, but still can't work out why it won't fire up!!

                    Comment

                    • alihomee
                      Badcaps Legend
                      • Dec 2012
                      • 1576
                      • malaysia
                      #6
                      Re: HP Compaq 6735S - No power / No charge

                      first of all check for 3v and 5valws on mobo .and also check 3v around bios chip

                        Comment

                        • fddizon
                          Badcaps Veteran
                          • Sep 2011
                          • 555
                          • Philippines
                          #7
                          Re: HP Compaq 6735S - No power / No charge

                          Originally posted by sebuncle
                          Hello,i have the same problem on a hp 6735b .It will not start no lights.
                          I looked on Q500 after power connector pins 1 to 4 have 19v and pins 4 to 8 have 0v. If I shunts pin 1 with 5 the laptop starts and works normally with the power button. If I remove the shunts intensity drop and the laptop shutdown . i don't find the real failure
                          find whats holding the pin 4 (gate) voltage. it should have 3 to 5 volts

                            Comment

                            • spleenharvester
                              Badcaps Veteran
                              • Mar 2010
                              • 902
                              • UK
                              #8
                              Re: HP Compaq 6735S - No power / No charge

                              Check the comparator circuit. Are you using a genuine HP adapter? It sends some kind of special signal which pulls a line (I think it's [edit see below]? but I can't remember) low, which allows VIN to reach the rest of the laptop.

                              Though personally, I have worked with several of these boards, and they are all utter crap. They will quit working completely if you sneeze on them.

                              EDIT: Just found my old thread, it's LIMITsignal:

                              Last edited by spleenharvester; 09-01-2013, 05:33 PM.
                              Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

                                Comment

                                • majoras54
                                  New Member
                                  • Mar 2017
                                  • 3
                                  • algeria
                                  #9
                                  Re: HP Compaq 6735S - No power / No charge

                                  HP Compaq 6535s 6735s Laptop Schematic

                                    Comment

                                    • majoras54
                                      New Member
                                      • Mar 2017
                                      • 3
                                      • algeria
                                      #10
                                      Re: HP Compaq 6735S - No power / No charge

                                      Originally posted by majoras54
                                      HP Compaq 6535s 6735s Laptop Schematic
                                      Attached Files

                                        Comment

                                        • hyditech
                                          Badcaps Veteran
                                          • Jun 2012
                                          • 272
                                          • nigeria
                                          #11
                                          Re: HP Compaq 6735S - No power / No charge

                                          Change the kbc chip

                                            Comment

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